Hydraulic amplifier



y 1, 1955 Htw. AVERY 2,709,421

HYDRAULIC AMPLIFIER Filed July 29, 1952 2 Sheets-Sheet 1 III/,IIIIIIIIII 4/ Fig.2. 4!

Inventor: Howard. W. Aver-y, by "EM 2. W

His At; orn ey.

y 1955 H. w. AVERY 2,709,421

HYDRAULIC AMPLIFIER Filed July.29, 1952 2 Sheets-Sheet 2 In vent or: Howard w. ver

by W6.

His Attorney.

HYDRAULIC AWLIFIER Howard W. Avery, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 29, 1952, Serial No. 301,444

13 Claims. (Cl. 121-41) This invention relates to hydraulic amplifier devices and systems and more particularly to such systems in which a control member may be moved a small distance by a relatively weak force to obtain proportional movement of a controlled member over a greater distance or with an amplified force or both.

One of the applications for hydraulic amplifiers has been in controlling hydraulic fluid flow to a hydraulic motor in accordance with a relatively weak electric signal. In a system which is used in such an application, the electrical signal may position a hydraulic control member by means of one or two electrical solenoids, and a hydraulic controlled member which is positioned in repsonse to the control member may in turn control the hydraulic fluid flow to a hydraulic load device such as a hydraulic motor. This is the application for which a number of prior hydraulic amplifier structures, as well as the structure and system of the present application, have been devised. Hydraulic amplifier systems of this type may sometimes be referred to as two-stage hydraulic servo systems. One of the major problems in the hydraulic amplifier is to obtain a proportional movement between the controlled member and the control member. Each of these members may take the form of hydraulic pistons, the control member generally being the smaller of the two and sometimes being referred to as a pilot valve. Several satisfactory solutions to this problem have been devised and the system disclosed in Patent 2,5 82,088 issued January 8, 1952, to Earle R. Walthers and assigned to the same assignee as the present application is an example of these.

The system disclosed in the Walthers patent employs hydraulic pressures applied to the ends of a controlled piston member which may be unbalanced by adjustment of a control valve member. The resultant force of the unbalance is opposed by centering springs on the controlled piston. This system provides generally satisfactory operation, although variations in the pressure level of the hydraulic fluid supply source provide a regulation effect, since the output motion is in response to hydraulic pressures in opposition to springs. Also, the amplification of movement between the control valve and the controlled piston is limited to a certain extent by the limitations in travel of the springs and by the build-up in force necessary to overcome the spring force for large movements of the controlled piston away from a central null position. However, the most serious limitation for applications where extremely fast response is required is that in this system there is a certain lag in response which results in unfortunately low natural frequencies of oscillation, causing serious instability problems when very sudden changes in input signal are encountered or if the input signal oscillates near the natural frequency. One methodof obtaining a faster response system with less lag and a resulting stability with high amplification is by employingan electrical position-indicating device connected to the controlled piston. The electrical position signal so obtained is amplified in an electrical amplifier, and connected to oppose the input signal to a solenoid, which reference should be ice may be used to provide the input signal for the control member, to thereby obtain a high gain electrical follow-up loop. Such a system will provide satisfactory operation where fast response is necessary, although the additional complexity of an electrical follow-up system is obviously undesirable.

In hydraulic amplifier servo or positioning systems, as they may be variously called, as in any other amplification system, it is generally obviously desirable to obtain a maximum amplification with a minimum time lag between the input and output in order to permit stable operation with high rates of signal change. In addition, reliable maintenance-free operation and simple construction permitting low manufacturing costs are obviously very desirable.

Accordingly, it is an object of this invention to provide an improved hydraulic amplifier having extremely fast response Without the added complexity of a nonhydraulic follow-up system.

Another object of this invention is to provide an improved hydraulic amplifier which not only has a greatly enhanced force amplification, but which also provides a very high position amplification.

Another important object of this invention is to provide a hydraulic amplifier in which the operation is substantially independent of normal variations in hydraulic fluid supply pressure.

A still further object of the invention is to provide an improved hydraulic amplifier which is particularly characterized by simplicity resulting in low manufacturing cost and having a compact structure and minimum weight. Further objects and advantages will be apparent from the following description.

In carrying out the above objects of this invention, a preferred structure may be employed in which a controlled member is positioned in response to a balance of forces of hydraulic fluid in chambers surrounding the ends of the member. Variations in the pressures of each chamber are governed by control of a continuous flow of hydraulic pressure fluid therethrough. A control valve member inversely controls the fluid flow through the respective chambers upon movement in response to an input signal, and the controlled member includes valve devices which may be in the form of capillary passages of variable length to inversely control the flow of fluid through the respective chambers upon movement thereof in a direction to rebalance the chamber pressures. obtained when the movement of the controlled member is essentially proportional to the movement of the control member.

For a more complete understanding of this invention, made to the following specification and the accompanying drawings in which:

Fig. 1 is a schematic partial sectional view of a system employing a preferred embodiment of the hydraulic amplifier of this invention in which the valve devices of the controlled member comprise annular capillary passages around undersized end lands.

Fig. 2 is a view corresponding to the upper portion of Fig. 1 showing an alternative embodiment of the invention.

Fig. 3 is a view corresponding to Fig. 1 of a second alternative embodiment of the invention.

Referring more particularly to Fig. 1, there is shown a system including a hydraulic amplifier having a control piston 10 and a controlled piston 11. In this system the control piston 10 is shown as connected and arranged for displacement in response to an unbalance in electrical signals supplied to solenoids 12 and 13, and. controlled piston 11 is connected to control a supply of hydraulic. device such as a load piston :14. Piston 10 may be variously referred to below as a fluid for movement of a load control member, a control valve, a pilot valve, or a first- Complete rebalance is v stage valve. Piston 11 may likewise be variously referred to as a controlled member, a controlled valve, or a secondstage valve. Pistons it and 11 may be supported within a common housing 15, although separate housings could obviously be employed if remote positioning were desired. The pistons iii and 11 may be respectively mounted within cylindrical bores 16 and 17 in housing by means of hardened cylindrical sleeves 1% and 1? which directly support the pistons. The ends of bore 17 are closed in, such as by end plates 20 and 21 to form control pressure chambers 22 and 23. Controlled piston 11 includes end lands 24 and in communication with the respective pressure chambers 22 and 23 for piston movement in response to differences (or an unbalance) in the pressures therein.

The valve lands 24 and 25 are each diameter ap preciably smaller than the inner bore of the valve sleeve 19 so as to provide a restricted passage for hydraulic fluid at each of the locations respectively indicated as 26 and 27. These annular passages ray be referred to below as capillaries although it will be understood that the dimensions of the openings may be substantially larger than the usual dimensions associated with the word capillary in the botanical sciences. in the present application the term capillary merely means a restricted passageway having an appreciable length. In such a restricted passage, the restriction to flow is dependent to a large degree on the length of the passage as well as the crosssectional area thereof. it will be obvious in the present invention that the capillaries 26 and 27 each vary in length as the piston 11 is displaced from a null central position shown, and the resistance to fluid ilow of these passages thereby is varied.

Hydraulic pressure fluid is supplied from a suitable source (not shown) through a conduit 28 and ports 29 and 3G in sleeve 1'9 to the pressure chambers 22 and 23 through capillaries 26 and 27. Hydraulic fluid may be discharged from pressure chambers 22 and 23 through conduits 31 and 32 which are connected through ports and 34 of the control valve sleeve 18 to end lands 35 and 36 of control valve 1%. Fluid is continuously passed by the end lands 35 and 36 and enters the central bore of sleeve 18 from which it is discharged through a central sleeve port 37 which is connected through a central housing opening 38 to a conduit 39 for return to a suitable hydrauiic fiuid reservoir (not Shown). The end lands 35 and 56 of control valve It are underlapped so as to leave both ports 33 and 34- open when the valve is in a central null position. These openings are changed inversely upon any movement of valve 10 away from the central position.

Since solenoids i2 and 13, which determine the positioning of control piston 10, are of substantially identical structure, only solenoid 12 is shown in sectional detail. Each of these solenoids may include an outer housing which is fastened to main housing 15 and having a solenoid winding 40 concentrically arranged with respect to the valve bore 16 and suitably insulated and sealed by an insulating spool 41. The winding 40 includes outgoing electrical connections 42 for the reception of electrical control signals. Centrally within the winding 40 a solenoid plunger 43 of magnetic material is supported by spring members 44 which also bias the plunger and a plunger stem 45 against the end land 35 of piston. 10. It will be understood that corresponding springs for solenoid 13 also bias the solenoid l3 plunger stem against control valve end land 36. Piston 10 is thereby spring biased to a central null position. Hydraulic pressures within the solenoid enclosures and on the outer ends of end lands 35 and 36 which may be due to leakage at those lands are equalized by a connecting passage 16a. A drain line connection (not shown) is also preferably provided from passage 160, or from one of the solenoid enclosures.

The controlled valve 11 includes intermediate lands 24a and 25a and a central land 46 which control the entrance and exit of hydraulic pressure fluid from ports 29 and 3% into the central portions of the inner bore of valve sleeve 19 enclosed by lands 24a and 25a and the exit of fluid from those spaces to the central discharge conduit 38. These central bore spaces flanking the two sides of valve center land 46 are respectively connected through conduits 47 and 48 to chambers formed by a power piston housing and separated by the power piston 14. It will be seen therefore that a given displacement of controlled piston it will result in a given rate of hydraulic fluid fiow through the conduits 47 and 48 and a resulting given rate of movement of power piston 14. Obviously piston 14 could be replaced by any other type of hydraulic motor or load for which the direction and speed of movement would be controlled by the position of piston 11.

Operation With pistons itiand 11 both in the central null position as shown, capillaries 2s and 27 at the end lands 24 and 25 are of equal length, and provide equal obstructions to the flow of hydraulic fluid. Likewise, the openings at ports 33 and 34 permitted by end lands 35 and 36 of piston it? are equal so as to provide identical obstructions to the flow of hydraulic pressure fluid. Under these conditions, a continuous equal flow of hydraulic fluid is attained through each of the chambers 22 and 23. However, if there is an unbalance in the electrical signals supplied to solenoids 12 and 13, such as a stronger signal supplied to solenoid 2, for instance, control piston 10 is moved to the right and port 33 is partially closed by land 35 while port 34 is partially opened by land 36 and the pressure drop at port 33 rises while that at port 34 falls. The pressure within chamber 22 is thus increased and the pressure in chamber 23 decreased. This unbalance of pressures forces piston 11 to the right, increasing the length of capillary 26 and decreasing the length of capillary 27 so that the pressure drop across capillary 26 rises, while that across capillary 27 fails. Piston 11 thus moves far enough to increase the pressure drop at capillary 26 and decrease the pressure drop at capillary 27 to bring the pressures of chambers 22 and 23 back into balance. The piston 11 will thus come to rest in a new, displaced position proportional to the displacement of piston 13. At this new position piston 11 connects port 30 to conduit 48 to provide for a greater pressure on the right-hand side of power piston 14 to cause a continuous movement thereof to the left. Fluid displaced by piston 14 is discharged through conduit 47 and out past center land 46 into discharge conduit 38.

While the valve lands 35 and 36 completely close oil the portions of ports 33 and 34 which are covered, the corresponding valve portions of piston 11 constituted by the capillaries 2s and 27 depend for their action on the change in capillary length. The travel of piston 11 required to rebalance the system is therefore much greater than the initial displacement of piston 10 causing the unbalance. Because of this characteristic, the present bydraulic amplifier is said to provide a high position amplification.

Since the maintenance of a particular pressure in either of the chambers 22 or 23 depends upon a continuous flow at an undisturbed rate through that chamber, it is obvious that a control movement of piston 10 which alters the flow rate immediately changes the pressure relationships Within those chambers without any appreciable time lag. Repositioning of the controlled piston 11 is therefore obtained very promptly. The follow-up operation or proportional movement of the controlled piston is not only obtained with a very fast response, but withoutthe necessity for any centering springs on the controlledpiston and without any connection other than the hydraulic fluid itself. to provide the proportional movement. Thisfeature permits a very compact, simple, and light-weight design.

Since this system depends upon a balance of pressures in two parallel hydraulic fluid paths, ordinary variations in supply pressure which equally alfect both paths will not change the characteristics of operation.

In Fig. 2 there is shown an alternative embodiment of the invention in which the capillary passages 26 and 27 are provided by pins 51 and 52 mounted on the ends of the controlled piston 11 which cooperate with separate small bore sleeves 53 and 54 fitted into appropriate openings in end plates and 21. The sleeves 53 and 54 may be preferably axially adjustable by means of adjusting screw members 55' and 56. Fluid connections from conduit 28 to the capillaries are provided by separate conduits 57 and 58. The remainder of the structure and the operation of Fig. 2 are substantially identical to that shown and described above for Fig. l. The main exception is that conduit 39 must now be the inlet and 28 the discharge conduit. This is true because the change in length of either of the capillaries 26 or 27 is in an opposite sense for a given direction of movement of piston 11; for instance, when piston 11 moves to the right in Fig. 1, capillary 26 increases in length whereas when piston 11 moves to the right in Fig. 2, capillary 26 decreases in length. Reversing the input and output connections therefore provides for correct, stable operation by reversing the fluid flow through chambers 22 and 23 since piston 11 movement must always rebalance the system. Also in Fig. 2 the end lands 24 and 25 of piston 11 have been combined with the intermediate lands 24a and 25a in the new conventional end lands 59 and 60.

Fig. 3 is a further modification, similar to Fig. 2, but in which pins 61 and 62 are attached to the cover plates 20 and 21 and extend into central bores 63 and 64 within piston 11 to provide the capillaries 26 and 27. The direction of flow through chambers 22 and 23 is the same as in Fig. 2 because the capillary change is the same for piston 11 movement. The fluid passing through the capillaries 26 and 27 from chambers 22 and 23 enters the central bores 63 and 64 of piston 11 and is discharged through radial ports 65 and 6a in end lands 5 and 60 to ports 29 and 38 and conduit 28. In other respects, the structure of Fig. 3 corresponds to those previously described for Figs. 1 and 2.

The pin capillary arrangements of Figs. 2 and 3 have the advantage over the arrangement of Fig. 1 that for a given cross-sectional area of the annular capillary the minimum opening can be greater, since the diameter of the annulus is smaller. This permits easier passage of solid particles of foreign material which may be present in the fluid. The centering adjustments provided by screw members 55 and 56 are also an advantage, but these structures are also a little more complicated and therefore more diflicult and expensive to manufacture.

The reduced diameter end lands 24 and 25 of Fig. 1, the pins 51 and 52 of Fig. 2, and the pins 61 and 62 of Fig. 3 may be referred to generically below as plungers. Likewise, the structures surrounding these plungers to form the annular capillary passages 26 and 27 in each of the three figures may be generically referred to as annular members.

While certain preferred embodiments of the invention have been shown, it will be understood that various changes and modifications may be made by those skilled in the art without departing from the true spirit and scope of the present invention. The scope of the invention is therefore intended to be limited only by the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A hydraulic positioning system comprising a control member and a controlled member, housing structure surrounding and supporting each of said members, at least two hydraulic fluid conduits interconnecting said members for conveyance of hydraulic pressure fluid under varying pressures for positioning of said controlled memher in accordance with the position of said control memher, a hydraulic pressure fluid inlet at one of said members, a fluid outlet at the other of said members, each of said members including passages to said conduits having restrictions variable upon member movement, the restrictions from at least one'of said members being in the form of constant cross-section capillaries of a length variable in accordance with the movement thereof.

2. A hydraulic servo system comprising a housing structure enclosing at least one control pressure chamber, a control valve member and a controlled valve member in communication with said chamber for control of hydraulic fluid flow therethrough, one of said members being connected to a hydraulic pressure fluid inlet for control of admission of fluid to said chamber and the other of said members being connected to a fluid outlet for control of discharge of fluid from said chamber, said controlled valve member including a fluid flow control portion and an operating surface in communication with said chamber for movement of said controlled member in response to changes of pressure therein, said fluid flow control portion and a cooperating portion of said housing structure defining a capillary passage of uniform cross-sectional area and of a length and resulting flow resistance variable upon movement of said controlled.

member.

3. A self-balancing hydraulic follow-up system which is independent of supply pressure variations comprising a housing structure enclosing a cylindrical cavity, a don ble ended piston reciprocally mounted within said cylinder and defining two control pressure chambers with the respective ends thereof, said piston being positionable in response to differences in the pressures Within said respective chambers, inlet and outlet conduits connected to each of said chambers for providing a flow of hydraulic pressure fluid therethrough, separate inlet and outlet conduit flow control structures respectively connected to a source of hydraulic pressure fluid and a low pressure return line and respectively arranged to concurrently control the flow through both inlet and both outlet conduits, each of said flow control structures being arranged to inversely adjust the flow through the respectiye associated conduits upon movement thereof, one of said flow control structures comprising valve elements forming uniform cross-section flow restrictive passages respectively connected to the chamber defining ends of said piston and movable therewith to vary the length of said passages, and an input signal responsive positioning device connected to position the other of said flow control structures.

4.A symmetrical continuous flow self-balancing hydraulic servo system comprising a control valve biased to a null position and movable in either direction therefrom in accordance with an input signal, a controlled piston and i a cylindrical housing supporting said piston and defining pressure chambers with the ends thereof, fluid conduits interconnecting said control valve and said pressure chambers. for providing a flow of hydraulic pressure fluid through said chambers, said control valve being arranged upon displacement from said null position to unbalance the flows and pressures of said chambers, said piston being movable in response to said unbalance of pressures, said piston including chamber fluid flow restrictive control devices of uniform reduced cross-sectional area and adjustable in length upon movement thereof for rebalancing said chamber pressures.

5. A hydraulic positioning system comprising a cylindrical housing having closed end chambers, a piston mounted within said housing in communication with said chamber for reciprocal positioning movement in response to an unbalanced condition of the fluid pressures within said chambers, a source of hydraulic pressure fluid connected for providing a continuous flow through each of said chambers, each end of said piston including a member communicating with one of said chambers defining a capillary passage of unvarying and uniform crosssectional area with an associated portion of said housing, said capillary passages having a length and flow resistance variable in response to piston movement for inverse adjustment of flow through said respective chambers to rebalance the pressures thereof, and a control valve connected to said chambers for unbalancing the fluid flows and pressures upon movement thereof to obtain corresponding desired piston displacements.

6. A hydraulic force and position amplifier comprising first and second reciprocable devices, a hydraulic pressure fluid inlet at one of said devices and a fluid outlet at the other of said devices, separate fluid conduits extending from said first device to the respective ends of said second device, each of said devices including separate flow control valve apparatus for controlling the division of fluid flow from said inlet connection to said outlet connection between said conduits in accordance with the displacement thereof from a central null position, said second device being movable from said null position in response to pressure differences between said conduits for an unbalanced condition of flow therethrough, said valve apparatus of said second device comprising an annular member and a plunger member arranged therein to define an annular capillary passage of uniform cross-section at each end thereof, one of each pair of said last mentioned members being connected to said second device for movement therewith and the other member of each pair being fixed with relation to said second device to thereby vary the length of said annular capillary passages upon movement of said second device.

7. A self-balancing continuous flow hydraulic servo system comprising a housing having a cylindrical bore and closed ends, a piston mounted within said cylindrical bore and defining two pressure chambers with said closed ends, said piston being movable in response to an unbalance of pressures within said chambers, common inlet and outlet conduits for conveying hydraulic pressure fluid to and from said chambers, a control valve connected between one of said conduits and said chambers for inversely adjusting the respective rates of fluid flow therethrough upon movement thereof to unbalance said chamber pressures, and flow control apparatus defining constant cross-section flow restrictions associated with each end of said piston and movable therewith to vary the length of said restrictions and respectively connected between said chambers and the other of said conduits for rebalance of said pressures by readjustment of said flows.

8. A self-balancing continuous flow hydraulic servo system comprising a housing having a cylindrical bore and closed ends, a piston mounted within said cylindrical bore and defining two pressure chambers with said closed ends, said piston being movable in response to an unbalance of pressures within said chambers, common inlet and outlet conduits for conveying hydraulic pressure fluid to and from said chambers, control valve connected between one of said conduits and said chambers for inversely adjusting the respective rates of fluid flow therethrough upon movement thereof to unbalance said chamber pressures, flow control devices associated with each end of said piston, each of said devices being connected between the associated chamber and the other of said conduits and comprising a plunger member and an annular member surrounding said plunger member to define an annular capillary passage of constant cross-section therewith, one of said members comprising a portion of said housing and the other of said members comprising a portion of the associated end of said piston for variation of the length of said capillaries upon movement thereof for re .olance said pressures by readjustment of said flows.

9. The combination of claim 8 in which each of said annular members comprises a portion of said cylindrical bore and each of said plunger members comprises an end land of said piston having a reduced outer diameter.

10. The combination of claim 8 in which each of said annular members comprises a portion of said housing and each of said plunger members comprises a pin portion of the associated end of said piston extending through the associated chamber into said annular member.

ll. The combination of claim 8 in which each of said annular members comprises the associated end or" said piston having an end opening therein and each of said plunger members comprises a pin portion, of said housing extending through the associated chamber and into said end opening.

l2. A self-balancing continuous flow hydraulic servo system comprising a housing having a cylindrical bore and closed ends, a piston mounted within said cylindrical bore and sing two pressure chambers with said closed ends, said piston being movable in response to an unbalance of pressures within said chambers, means for providing a flow of hydraulic pressure fluid through said chambers, a control valve means connected to both of said chambers for inversely adjusting the respective rates of fluid flow therethrough upon movement thereof to unbalance said chamber pressures, annular members of uniform diameter supported in said housing at each of said chambers and flow control plungers of uniform diameter axially movable with said piston for inverse variable penetration of said annular members for rebalance of said pressures by readjustment of said flows.

13. A hydraulic servo system comprising a control valve and a controlled valve, a housing for enclosing and supporting said controlled valve having a cylinder bore therein, a cylinder sleeve mounted within said bore, said controlled valve comprising a piston reciprocably mounted within said sleeve and having ends normally protruding beyond the respective ends of said sleeve, said piston ends being comprised of end lands of reduced diameter to form annular capillary passages of variable length and constant cross-section with the associated ends of said sleeve, the ends of said housing bore being closed to form control pressure chambers at the ends of said controlled piston, a connection from a source of hydraulic pressure fluid to said capillary passages for control of the admission of fluid to said chambers, and connections from said chambers to said control valve and from said control valve to a discharge conduit for the control of the discharge of fluid from said chambers by said control valve.

References Cited in the file of this patent UNZTED STATES PATENTS 787,136 Warren Apr. ll, 1905 1,638,102 Roucka Aug. 9, 1927 1,814,827 Caughey July 14, 1931 2,233,319 Lozivit et al Feb. 25, 194l 2,396,951 Horstmann Mar. 19, 1946 2,582,088 Walthers Jan. 8, 1952 FOREIGN PATENTS 47,236 France Nov. 25, 1936 (2nd addition to No. 801,509) 

